1. Field of the Invention
This invention relates to detergent formulations. In particular, this invention relates to defoaming detergent compositions especially suitable for use in automatic dishwashing machines. And specifically, this invention relates to a defoaming phosphate ester - low-foaming, nonionic surfactant combination particularly useful in automatic dishwashing detergents.
2. Brief Description of the Prior Art
The generation of foam in automatic dishwashing machines has been a problem facing consumers and industry for many years. Development of excessive foam in the dishwashing machines can result in machine overflow and reduced rotor speeds of the perforated spray arms in the dishwasher. Even moderate foaming reduces the efficiency of the automatic dishwashing machine by retarding the mechanical action of the water spray and by reducing the rate of rotation of the spray arm.
The terms "foam" and "foaming" as used herein refer to the combination of entrapped air and surface active material at the surface of an aqueous solution. Such surface active material can come from the soil on the dishes or from surfactants contained in the dishwashing detergent. A particularly troublesome source of foam is proteinaceous soil, especially raw egg soil.
Many of the present automatic dishwashing detergent manufacturers have tried to overcome this foaming problem by adding low-foaming surfactants and foam-suppressants or defoamers to their detergent formulations. U.S. Pat. Nos. 3,314,891 and 3,595,968 show attempts to solve this problem with types of additives different than the present invention to dishwasher detergents. The former patent describes several low-foaming, nonionic surfactants combined with a stearyl or oleyl acid phosphate defoamer. The second patent describes another dishwasher detergent additive which also contains a low-foaming, nonionic surfactant in conjunction with a phosphate ester defoamer. The compositions disclosed in both of these patents are said to be effective for reducing the foam caused by the presence of proteinaceous soil.
Another U.S. Pat. No. 3,741,912 is similar to the above two patents. It discloses the addition of an oxyethylated amine to the nonionic surfactant-phosphate ester additive in order to prevent the two compounds from separating during storage which causes problems in subsequent handling and formulating.
However, a need still exists in this particular art for a combination of nonionic surfactants and alkyl phosphate esters which can be employed as an effective dishwashing detergent additive that has low-foaming and defoaming properties, will not separate from each other during storage, can be formulated with several combinations of inorganic detergent salts (referred to sometimes as detergent "builders") and does not need an oxyethylated amine or other chemicals to prevent separation.